Coupled acoustic devices

An acoustic device, comprising:

• a first coupled resonator filter (CRF), a second CRF electrically coupled to the first CRF, and a compensating capacitor, Cb, electrically coupled to the second CRF,
• wherein each of the first CRF and the second CRF has a bottom FBAR, an acoustic decoupler formed on the bottom FBAR, and a top FBAR formed on the acoustic decoupler, wherein each of the bottom FBAR and the top FBAR has a bottom electrode, a piezoelectric layer formed on the bottom electrode, and a top electrode formed on the piezoelectric layer;
• wherein the first CRF has an input port and an output port electrically connected to first and second corresponding electrodes of the first CRF, respectively, such that the acoustic decoupler of the first CRF is located between the first and the second corresponding electrodes;
• wherein the second CRF has an input port, a first output port and a second output port electrically connected to first, second and third corresponding electrodes of the second CRF, respectively, such that the acoustic decoupler of the second CRF is located between the first corresponding electrode and both the second and third corresponding electrodes;
• wherein the output port of the first CRF is electrically connected to the input port of the second CRF;
• wherein for the first CRF, one of the bottom electrode of the top FBAR and the top electrode of the bottom FBAR is electrically connected to the input port and the other of the bottom electrode of the top FBAR and the top electrode of the bottom FBAR is electrically connected to the output port, and the top electrode of the top FBAR and the bottom electrode of the bottom FBAR are grounded, such that the bottom electrode of the top FBAR, the acoustic decoupler and the top electrode of the bottom FBAR operably define a feedback capacitor, Cp;
• wherein for the second CRF, one of the bottom electrode of the bottom FBAR and the top electrode of the top FBAR is electrically connected to the input port, wherein when the bottom electrode of the bottom FBAR is electrically connected to the input port, the top and bottom electrodes of the top FBAR are electrically connected to the first and the second output ports, respectively, and the top electrode of the bottom FBAR is grounded, and when the top electrode of the top FBAR is electrically connected to the input port, the bottom and top electrodes of the bottom FBAR are electrically connected to the first and the second output ports, respectively, and the bottom electrode of the top FBAR is grounded, such that the bottom electrode of the top FBAR, the acoustic decoupler and the top electrode of the bottom FBAR operably define an internal port-to-ground capacitor, C′p;
• and
• wherein the compensating capacitor Cb is electrically coupled between the top electrode of the top FBAR and the top electrode of the bottom FBAR when the bottom electrode of the bottom FBAR is electrically connected to the input port, and the compensating capacitor Cb is electrically coupled between the bottom electrode of the bottom FBAR and the bottom electrode of the top FBAR when the top electrode of the top FBAR is electrically connected to the input port.